He tells you at the website how it was collected. His name Steve Martin's and he is a ISF certified technician.
"Bit rates were calculated based on file sizes recorded by an HD Tivo. I'm very confident these numbers are accurate as I compared them to analysis of a recording of an OTA sample on DVHS and using TSReader Lite to analyze the resulting transport stream. The bitrates for the video and audio streams add up to what I'm computing. If you are interested in the math behind computing the bitrates, I've detailed it in a Blog Entry"
"Bit rates were calculated based on file sizes recorded by an HD Tivo. I'm very confident these numbers are accurate as I compared them to analysis of a recording of an OTA sample on DVHS and using TSReader Lite to analyze the resulting transport stream. The bitrates for the video and audio streams add up to what I'm computing. If you are interested in the math behind computing the bitrates, I've detailed it in a Blog Entry"